This invention is in the field of art relating to fluid compositions specialized and designed for use between two relatively moving surfaces in contact therewith for reducing friction therebetween and preserving the surface. Lubricant compositions of the invention contain a compound which has a calcium component linked to carbon through oxygen.
It is well known that lubricating oils tend to deteriorate under conditions of use in present day diesel and automotive engines with attendant formations of sludge, lacquer and resinous materials which adhere to the engine parts, particularly the piston ring, groove and skirt, thereby lowering the operating efficiency of the engine. To counteract the formation of these deposits, certain chemical additives have been found which when added to lubricating oils have the ability to keep the deposit forming materials suspended in oil so that the engine is kept clean and in efficient operating condition for extended periods of time. These agents are known in the art as detergent-dispersants. Metal organic compounds are particularly useful in this respect. One class of metal organic compounds which have been found so useful are the sulfurized normal and overbased calcium alkylphenolates. It is to be noted that the term "normal" employed hereinbefore and hereinafter denotes the ratio of the number of equivalents of calcium moiety to the number of equivalents of alkylphenol moiety is 1, that is, the calcium metal ratio is 1. The term "overbased" denotes ratio greater than 1.
Although the sulfurized calcium alkylphenolates of the past were effective detergent-dispersants, they were found to be somewhat less than satisfactory in that they were prone to oxidative deterioration resulting in the formation of corrosive products which attack the metal surface of the engines under severe operating conditions. Further under severe operating conditions, such as in diesel engine operations, the sulfurized calcium alkylphenolates form oxidation products which undesirably result in a substantial change in lubricant viscosity. In an effort to solve this problem, improved sulfurized calcium alkylphenolates containing lubricant compositions more resistant to oxidation were formulated as covered in U.S. Pat. Nos. 3,528,917, 3,549,534 and 3,761,414. However, with the ever increasing demands, the anti-pollution controls placed on today's engine oils, there is a continuing search for additives such as the sulfurized normal calcium alkylphenolates of even still further improved resistance to undesirable oxidation in engine operating conditions.